From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756658AbbCFT2b (ORCPT ); Fri, 6 Mar 2015 14:28:31 -0500 Received: from mail-ie0-f176.google.com ([209.85.223.176]:33823 "EHLO mail-ie0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932173AbbCFT20 (ORCPT ); Fri, 6 Mar 2015 14:28:26 -0500 MIME-Version: 1.0 In-Reply-To: References: <1425456048-16236-1-git-send-email-yinghai@kernel.org> <1425456048-16236-2-git-send-email-yinghai@kernel.org> <20150306135534.GD4259@pd.tnic> Date: Fri, 6 Mar 2015 11:28:25 -0800 X-Google-Sender-Auth: S2K_0P3SQ2nKVfuXpoJx4fQLPZQ Message-ID: Subject: Re: [PATCH v2 01/15] x86, kaslr: Use init_size instead of run_size From: Yinghai Lu To: Kees Cook Cc: Borislav Petkov , Matt Fleming , "H. Peter Anvin" , Bjorn Helgaas , Thomas Gleixner , Ingo Molnar , Jiri Kosina , Borislav Petkov , Baoquan He , Linux Kernel Mailing List , "linux-efi@vger.kernel.org" , "linux-pci@vger.kernel.org" , Josh Triplett , Andrew Morton , Ard Biesheuvel , Junjie Mao Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 6, 2015 at 10:55 AM, Kees Cook wrote: > On Fri, Mar 6, 2015 at 10:44 AM, Yinghai Lu wrote: > > I don't see how bss and brk are related to these sizes. Can you > explain how bss, brk, and initrd factor into these sizes? Those were > what run_size was created to represent. I don't want to accidentally > start stomping on bss and brk again. :) VO (vlinux) init size aka VO_INIT_SIZE already inlude that. Please check update version. commit e6023367d779 ("x86, kaslr: Prevent .bss from overlaping initrd") introduced one run_size for kaslr. We should use real runtime size (include copy/decompress) aka init_size. run_size is VO (vmlinux) init size include bss and brk. init_size is the size needed for decompress and it is bigger than run_size when decompress need more buff. According to arch/x86/boot/header.S: | #define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset) | #define VO_INIT_SIZE (VO__end - VO__text) | #if ZO_INIT_SIZE > VO_INIT_SIZE | #define INIT_SIZE ZO_INIT_SIZE | #else | #define INIT_SIZE VO_INIT_SIZE | #endif | init_size: .long INIT_SIZE # kernel initialization size Bootloader allocate buffer according to init_size in hdr, and load the ZO (arch/x86/boot/compressed/vmlinux) from start of that buffer. init_size first should come from VO (vmlinux) init size. That VO init size is from VO _end to VO _end and include VO bss and brk area. During running of ZO, ZO move itself to the middle of buffer at z_extract_offset to make sure that decompressor would not have output overwrite input data before input data get consumed. But z_extract_offset calculating is based on size of VO (vmlinux) and size of compressed VO only at first. So need to make sure [z_extra_offset, init_size) will fit ZO, that means init_size need to be adjusted according to ZO size. That make init_size is always >= run_size. During aslr buffer searching, we need to make sure the buffer is bigger enough for decompress at first. So use init_size instead, and kill not needed run_size related code.